Angular Diameters of the G Subdwarf μ Cassiopeiae A and the K Dwarfs σ Draconis and HR 511 from Interferometric Measurements with the CHARA Array

Using the longest baselines of the CHARA Array, we have measured the angular diameter of the G5?V subdwarf ??Cas?A, the first such determination for a halo population star. We compare this result to new diameters for the higher metallicity K0?V stars, ??Dra and HR?511, and find that the metal-poor star, ??Cas?A, has an effective temperature ( -->Teff = 5297 ? 32 K), radius ( -->R = 0.791 ? 0.008 R?), and absolute luminosity ( -->L = 0.442 ? 0.014 L?) comparable to those of the other two stars with later spectral types. We show that stellar models show a discrepancy in the predicted temperature and radius for ??Cas?A, and we discuss these results and how they provide a key to understanding the fundamental relationships for stars with low metallicity.

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